Born on March 30, 1762, in Lancaster County, Province of Pennsylvania, British America,[1] McNairy read law in 1788.

[1] He was a Judge of the Superior Court of Law and Equity, Mero District, starting in 1788.

[Note 1][2][1] He was nominated to the Territorial Court for the Southwest Territory by President Washington on June 7, 1790,[3] and was confirmed by the United States Senate on June 8, 1790, serving in that post until his appointment to the District of Tennessee.

[4] Following the admission of the Southwest Territory to the Union as the State of Tennessee on June 1, 1796, McNairy was nominated by President George Washington on February 17, 1797, to the United States District Court for the District of Tennessee, to a new seat authorized by 1 Stat. 496.

[1] He was confirmed by the United States Senate on February 20, 1797, and received his commission the same day.